Room-temperature hyperpolarization via polarization relay through rapid cocrystallization

Hyperpolarization of solids at room temperature using photoexcited triplet electrons [triplet dynamic nuclear polarization (DNP)] has been limited to a small number of solid-state systems, primarily those composed of molecules with exceptionally long nuclear spin-lattice relaxation times (T ₁). Here, we introduce HYCOR (HYperpolarization via COcrystallization and Relay), which is a polarization-relay strategy that enables the transfer of hyperpolarization generated by triplet DNP from a polarized mediator to target molecules through rapid cocrystallization. As a proof of concept, we demonstrate room-temperature ¹³C polarization of pyruvic acid (PyA), a benchmark molecule in hyperpolarization studies. In this approach, polycrystalline picolinamide (PAm) containing dispersed pentacene is hyperpolarized by triplet DNP, followed by rapid mixing with liquid PyA to induce cocrystallization. The resulting PyA-PAm cocrystals exhibit ¹³C polarization of up to 0.012% in the solid state and 0.0028% after dissolution at room temperature. Analysis of the polarization loss reveals that the efficiency of HYCOR is governed by a kinetic competition between cocrystallization and T ₁ relaxation. HYCOR provides a concept for extending triplet DNP to target molecules that are difficult to polarize directly.